Gel compositions comprising styrene-diene block copolymers and hydrocarbon oils wherein the copolymer constitutes up to about 30 parts by weight and the oil constitutes at least about 70 parts by weight are known in the art as well as various methods of preparing these compositions. Examples of such compositions and their preparation are illustrated in U.S. Pat. Nos. 4,369,284 and 4,618,213 to Chen; 3,827,999 to Crossland; 4,176,240 to Sabia; 3,485,787 to Haefele; and 3,676,384 to Lindlof; and in my copending application Ser. No. 801,018 filed Nov. 22, 1985 (equivalent to published European application 0224389) and now granted as U.S. Pat. No. 4,716,183. The disclosures of these patents and the copending application are incorporated herein by reference. The various compositions within this class of gels have different combinations of physical properties depending on the use intended for the gel.
A styrene-diene block copolymer of particular interest in the present invention is a poly (styrene-ethylene-butylene-styrene) triblock copolymer (SEBS triblock copolymers) which, when combined with sufficient plasticizer, such as a hydrocarbon oil, provides a gel composition having a cone penetration at least about 50, for example in the range of about 50 to at least 290, say about 300 (10.sup.-1 mm) (ASTM D217-82) and an ultimate elongation of at least 200% (ASTM D412). For example, in Chen U.S. Pat. No. 4,369,284 these triblock copolymers were melt blended with oils to produce a gel-like material which is meltable and useful for cast molding of shaped articles.
I have found that it is desirable to use these SEBS triblock copolymer-oil compositions in various applications, such as in U.S. Ser. No. 698,643 filed Feb. 6, 1985, the disclosure of which is incorporated herein by reference. However, these materials do not have satisfactory resistance to higher temperatures, i.e., at higher temperatures such as 90.degree. C. or higher and in some cases 100.degree. C. or higher, these materials may slump or flow in a manner that causes the material to lose its original shape and its original function. At these higher temperatures some of the prior art compositions also slump, flow and loose oil content which contaminates surrounding equipment.
Therefore, it is an object of this invention to produce SEBS triblock copolymer-oil compositions of the above type having heat resistant characteristics so that they will not lose their dimensional integrity at elevated temperatures.
In my U.S. Pat. No. 4,716,183 heat resistant gels are made by mixing a styrene-diene block copolymer and a hydrocarbon oil at an elevated temperature sufficient to cause the block copolymer to melt and disperse in the oil, and optionally also by crosslinking the resulting material by electron beam radiation. It is an object of this invention to provide improved heat resistant gels without the necessity of using electron beam radiation.
The patents cited above do not meet these objectives and do not disclose the desired heat resistant compositions. Crossland discloses similar block copolymers but are polyisoprene or polybutadiene block copolymers which are melt blended with oils at a temperature of 50.degree. to 250.degree. C. to produce compositions which are meltable and castable; i.e. they have a very low viscosity at higher temperatures such as 200.degree. C. Haefele contains disclosure similar to Crossland wherein the block copolymers and oil are melt blended at 160.degree. C., and Lindlof contains similar disclosure wherein the polymers are melt blended with the oil at 175.degree. C.
SEBS copolymers have typically not been used with high loadings of oil but have usually been limited to about 50 parts by weight oil and about 50 parts by weight SEBS block copolymer, as illustrated in U.S. Pat. No. 4,556,464 to St. Claire.
Chen, U.S. Pat. No. 4,369,284, however, uses 100 parts by weight SEBS block copolymers with about 300 to about 1600 parts by weight oil to produce meltable, castable compositions by melt blending at about 150.degree. C. to 200.degree. C. Chen teaches that the use of the SEBS block copolymer with low molecular weight oils melt blended at the desired temperature produces the meltable, castable composition having at least 1600% elongation and tensile strengths in the range of about 12 to about 145 psi.
There is no disclosure or suggestion in these cited references of any composition or how to obtain any composition of these types which would be heat resistant and have a viscosity of at least 200 poise at 200.degree. C.